CODEWITHSUNDEEP
c++c++11
user2757083
user2757083

Reputation:

Overloading operator>>: cannot bind ‘std::basic_istream<char>’ lvalue to ‘std::basic_istream<char>&&’

I have the operator in my header as such:

friend std::istream& operator>> ( std::istream& is, StudentRecord& sr );

and in my class:

std::istream& operator>>(std::istream& is ,  StudentRecord& sr){
    is >> sr.name >>std::ws>> sr.surname>>std::ws>>sr.studentNumber>>std::ws;
    getline(is, sr.classRecord);
    return is;
}

However, I get the following error:

std::basic_istream<char>’ lvalue to ‘std::basic_istream<char>&&

in a database class:

void Database::read(string f)
{

    studRcrds.clear();
    std::ifstream in(f.c_str());
    string studLine;
    while (!(in.eof()))
    {

        getline(in,studLine);
        std::istringstream sin(studLine);
        StudentRecord newStudent();
        sin >> newStudent;
    }
}

Upvotes: 0

Views: 5820

Answers (2)

Advisor
Advisor

Reputation: 1

You may also change your getline function:

istream& getline(std::istream& is, StudentRecord& sr)

without using a newStudent object.

Upvotes: -2

Jonathan Wakely
Jonathan Wakely

Reputation: 171443

The error is a bit confusing, but it means there is no operator>> that can be used for sin >> newStudent;

That is because you have declared newStudent as a function (see most vexing parse). The wording of the error is because there is an overload for rvalue streams that accepts anything on the right-hand side:

template<typename CharT, typename TraitsT, typename T>
basic_istream<CharT, TraitsT>&
operator>>(basic_istream<CharT, TraitsT>&& istr, T&&);

and because there is no matching operator for the function type of newStudent it tries to call that overload, which can't bind an rvalue-reference to sin.

The fix is to avoid the most vexing parse:

StudentRecord newStudent;

or:

StudentRecord newStudent{};

or:

StudentRecord newStudent = newStudent();

or similar. With that change newStudent has the right type and so can use your operator>> overload.

Upvotes: 9

Related Questions